Phosphor suspension for dip-coating metallic segments

ABSTRACT

A phosphor suspension for dip-coating metallic segments of a display device to provide a layer of phosphor thereon. The suspension is an aqueous solution containing a first preliminary binder such as polyvinyl alcohol, a second permanent binder such as sodium or potassium silicate, a given quantity of phosphor particles, a bubble eliminating agent selected from the group of lower primary alcohols having from one to five carbon atoms, a wetting agent such as sodium oleate, and a high-boiling solvent such as ethylene glycol. The suspension is applied to a suitable substrate such as a flexible sheet of vinyl and allowed to drain to leave a layer of suspension thereon. The metallic segments have the side to be coated brought into contact with this layer and are pressed thereinto and then removed for drying and subsequent processing.

Speigel et al.

Oct. 2, 1973 PHOSPIIOR SUSPENSION FOR DIP-COATING METALLIC SEGMENTS inventors: Kenneth Speigel; Robert F. Wilson,

both of Seneca Falls, N.Y.

Assignee: GTE Sylvania Incorporated, Seneca Falls, N.Y.

Filed: June 21, 1971 Appl. No.: 155,235

U.S. Cl.. 252/3013 R, 117/335 C, 117/33.5 L Int. Cl C091: 1/02 Field of Search 252/3013 R;

7 References Cited UNITED STATES PATENTS Reed et a1 Friedman et al.

Primary Examiner-Daniel E. Wyman Assistant ExaminerA. P. Demers Attorney-Donald R. Castle et al..

[57] ABSTRACT A phosphor suspension for dip-coating metallic segments of a display device to provide a layer of phosphor thereon. The suspension is an aqueous solution containing a first preliminary binder such as polyvinyl alcohol, a second permanent binder such as sodium or potassium silicate, a given quantity of phosphor particles, a bubble eliminating agent selected from the group of lower primary alcohols having from one to five carbon atoms, a wetting agent such as sodium oleate, and a high-boiling solvent such as ethylene glycol. The sus pension is applied to a suitable substrate such as a flexible sheet of vinyl and allowed to drain to leave a layer of suspension thereon. The metallic segments have the side to be coated brought into contact with this layer and are pressed thereinto and then removed for drying and subsequent processing.

1 Claim, N0 Drawings PHOSPI-IOR SUSPENSION FOR DIP-COATING METALLIC SEGMEN'IS BACKGROUND OF THE INVENTION This invention relates to a phosphor suspension and more particularly to a phosphor suspension for dipcoating metallic segments to be utilized as illuminable anode displays in an evacuated display device. Still more particularly, the invention relates to a phosphor suspension employing two binders, a wetting agent, a bubble eliminating agent and a solvent having a high boiling point to control the drying time of the segments.

Metallic segments to be coated for use in evacuated display devices have been previously coated by spraying or by painting with a brush. These prior art techniques are time consuming and difficult to control as to thickness of the phosphor coating, a critical factor since uneven thicknesses of coating will provide uneven light output in the finished device. It would be advantageous and an advance in the art if a phosphor suspension could be developed to allow dip-coating of metallic segments to provide a uniform layer of phosphor with good reproducibility.

OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of this invention to obviate the disadvantages of the prior art.

It is another object of the invention to enhance the art of coating metallic segments with phosphor.

These objects are accomplished in one aspect of the invention by the provision of a suspension for dipcoating metallic segments which comprises a given quantity of phosphor particles having an average particle size of less than 5 microns. A wetting agent selected from the groupconsisting of alkali metal and ammonium salts of upper alkenyl monohydric acids containing from 12 to 30 carbon atoms is included to insure complete wetting of the metallic segments. First and second binders such as PVA and sodium or potassium silicate are included, the first binder preliminarily holding the suspension in place but being removed before final processing and the second binder remaining after final processing. Also included are a bubble eliminating agent such as isopropyl alcohol and a high-boiling solvent which rcduces the evaporation rate of the suspension during coating. This suspension provides extremely uniform coating of metallic segments and is superior to either spraying or painting in reproducibility.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims.

Referring now to the invention with greater particularity, a phosphor suspension according to the invention can be formed as follows.

In a ball mill or other suitable mixer place 10 ml PVA (6% solution in H,O as first binder) 30 gms phosphor (phosphate coated P15) 4 ml lsopropyl alcohol (as a bubble eliminating agent) 4 ml Ethylene glycol (as high-boiling solvent) 6 ml Potassium silicate (0.0054N in I-I,O as second binder) 0.11 ml Sodium oleate (0.02% in 11 0 as wetting agent) and mix thoroughly. Pebbles are not needed in a ball mill since no attrition is required. After mixing, the coating is ready for immediate use.

The first binder or PVA has a volatilizing temperature in the range of 400C to 500C and is removed from the coating by firing before final processing.

The bubble eliminating agent is selected from the group consisting of lower primary alcohols having from one to five carbon atoms; however, the isopropyl alcohol is preferred. The solvent can be selected from the group of higher alcohols; i.e., those having more than 5 carbon atoms. The actual selection will depend upon the length of drying time required.

The required wetting agent is selected from the group consisting of metal and ammonium salts of upper alkenyl monohydric acids containing from 12 to 30 carbon atoms; sodium oleate being a preferred embodiment.

The second or remaining binder is selected from the group consisting of sodium and potassium silicate.

To utilize this suspension in a dip-coating process it is preferred that the metallic segments to be coated be pre-assembled on a support with all of the segments lying in the same plane. Such a structure is shown in US. Ser. No. 82,705, filed Oct. 21, 1970, now abandoned and assigned to the assignee of the present invention. To apply the coating a thin, even layer of suspension is formed on a flat flexible surface. This can be accomplished by a drip and drain technique. For example, in one embodiment which has been employed a 1 inch X 6 inch strip of vinyl sheet was dipped in the suspension, drained vertically for one minute, then set down upon flat laboratory bench. The viscosity, surface tension, and drain time combine to produce a reproducible thin-layer of suspension. The metallic segments to be coated are then pressed down on the suspension, lifted and allowed to dry. The PVA is baked out of the coating at a temperature of between 400C and 500C before the coated segments are permanently assembled.

This suspension provides reproducible coatings having the required consistency to produce even light output and achieves results not heretofore obtainable by painting or spraying.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

l. A phosphor suspension for dip-coating metallic segments of a display device, said suspension comprising, in the indicated quantities or multiples thereof: an aqueous solution consisting essentially of about 0.1 1 ml sodium oleate solution, said sodium oleate solution comprising about 0.02% sodium. oleate in water as a wetting agent; a first binder comprising 10 ml polyvinyl alcohol solution which comprises about 6% polyvinyl alcohol in water; about 4 ml isopropyl alcohol as a hubble eliminating agent; about 4 ml ethylene glycol as a high boiling solvent; about 6 ml potassium silicate whichcomprises a 0.0054N potassium silicate in water as a second binder; and 30 grams of phosphor.

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